1. Field of the Invention
This invention relates to fluid seals and in particular to buffer seals for protecting face-type seals from excessive pressures.
2. Description of the Prior Art
In U.S. Pat. No. 3,180,648 of Bernard F. Kupfert et al, owned by the assignee hereof, an improved ring-type face seal is disclosed for sealing confronting surfaces of relatively rotatable parts. As disclosed therein, lubricant is introduced under pressure into the apparatus and the seals are adapted to provide improved fluid sealing against such pressure.
It has been found that, in certain applications of such seals, such as in conjunction with oil-cooled disc brakes, as disclosed in Elmer R. Bernson et al U.S. Pat. No. 3,072,220, and Curtis F. Cummins U.S. Pat. No. 3,136,389, owned by the assignee hereof, conditions may arise wherein relatively high back pressure may obtain tending to shorten the useful life of the seals. Illustratively, where such seals have been used in off-highway truck applications, the back pressures have been relatively low so that long, trouble-free life has been readily obtainable. Where the seals, however, are utilized in applications such as in connection with the rear wheel means of a tractor-scraper, several problems arise. The wheelbase of such tractor-scrapers is considerably longer than that of conventional trucks and, thus, relatively long transfer lines are required. It is preferable that such fluid transfer lines be of relatively small diameter to reduce the bulk of the lines crossing over the hitch portion of the apparatus. The increased length and reduced diameter of the fluid transfer conduits produces a substantial increase in the back pressure of the lubricating coolant delivered therethrough to the brake means.
Further, in such tractor-scraper apparatus, the diameter of the face seals required is substantially larger than that required in the truck applications, the increase being in the order of 8 inches to 15 inches and thereby requiring a somewhat less resilient seal, reducing the ability thereof to accommodate high back pressures for any protracted period of time.
Where the need for the lubricating coolant is intermittent, or the environmental temperature conditions are relatively low, increased viscosity in the lubricating coolant fluid causes further increase in the back pressure.
Further, tractor-scraper wheels are substantially larger than conventional truck wheels and, thus, relatively large disc brake elements are conventionally required. The increase in the surface area of the disc brakes further tends to restrict the lubricating coolant fluid flow through the apparatus, thereby again increasing back pressure and aggravating the back pressure problem as discussed above.
A number of prior devices have been developed for balancing pressures in fluid control devices. Illustratively, in Floyd S. Dadds et al U.S. Pat. No. 3,679,216, owned by the assignee hereof, a pressure-balanced track roller for underwater use is disclosed having piston or diaphragm means for maintaining face loads on the seal rings when the track roller is operated at substantial depths.
Additionally, Archibald S. Telfer U.S. Pat. Nos. 1,474,454 and 1,737,870, show a centrifugal pump utilizing pressure-balancing means; Kenton D. McMahan et al U.S. Pat. No. 2,575,923 shows a method and apparatus for pumping volatile liquids utilizing pressure-balancing means; and Robert W. Erikson et al U.S. Pat. No. 2,931,314 shows an air purging apparatus for pumps permitting purging of the air to atmosphere and rapid closure of the pressure responsive valve on pump shutdown.